The seven-time Tour de France champion, who has organized similar events in Los Angeles, Glasgow and Dublin, was staggered by the reaction after he used the micro-blogging site to invite the public to “come one, come all”.

“I personally don’t think that anyone will top the turnout we had today. That was a huge amount of people,” Armstrong said.

“The field stretched for kilometres and kilometres … when we turned back there was just streams of people.”

Riders gathered at Wigley Reserve outside Adelaide, venue for next week’s Tour Down Under, and followed Armstrong and McEwen along a coastal road to Semaphore Park and back again, a distance of about 30 kilometres (19 miles).

“It was chaos, but controlled chaos. It’s certainly the biggest one that I’ve been a part of,” said Armstrong. “It was cool. Everybody had a good time and more or less stayed safe.”

Several riders came off in the crush but there were no serious injuries, according to police.

“There was a lot of cyclists and it’s difficult to control when they’re in a bunch that big,” police traffic coordinator Harry McCallum told AFP.

“We saw a couple of people that had fallen off their bicycles but there was nothing that looked serious,” he added.

Armstrong, 38, will seek an eighth Tour de France title in July after coming out of retirement last year.

“I’m just surprised by the sheer numbers, this is out of control,” McEwen said.

The large turnout comes after thousands of fans mobbed golf megastar Tiger Woods at Melbourne’s Australian Masters in November, his last tournament before a string of affairs came to light.